This invention relates generally to positive displacement rotary compressors and pumps and specifically to screw compressors and pumps having rotors with identical pitch circle diameters and in which the lands and grooves of each rotor are of equal radius and are uniformly spaced and centered along the pitch circle.
2. Description of the Prior Art
From the earlier "Roots" type blowers to the more currently developed oil injection screw compressors, there has been considerable effort directed to refining and developing rotary pumps and compressors to achieve increased operating efficiency, reduce costs, and improve production techniques.
Prior to the introduction of the oil injected screw threaded compressors, it was necessary to manufacture the compressor rotors in such a manner as to provide sufficient clearance between rotor parts to reduce friction wear and allow for the heating effects on the mating components. Such clearance space required the rotors to be run at a greater rate to compensate for the lost compression efficiency of the system.
With the introduction of oil injection into screw compressors, not only was it possible to increase the compressor tolerances by providing lubrication to ease friction wear and cool the compressor components, but the oil increased efficiency by reducing the necessary clearance between the mating compressor rotors.
In an effort to further simplify the design of the screw compressor, a system or method of a single rotor drive was developed. In this type of operation, one rotor is driven solely by its engagement with another rotor which is connected to the compressor drive or motor. This system obviated the need for rotor timing gears or chains and resulted in even closer tolerances between the mating parts of the compressor rotors and thereby improved compressor efficiency.
Some examples of the prior art are U.S. Pat. Nos. 2,623,469 to Gray; 1,409,868 and 1,439,628 to Kier; 2,460,310 to Rathman; 30,159 and Re. 2,369 to Roots; and 2,622,787 to Nilsson.